A bush bearing is used to connect the stator and rotor of a motor. Generally speaking, in the manufacture, a sufficient amount of copper powder or iron powder or other material is pressurized and shaped to form a generally cylindrical hollow bearing. As shown in FIG. 1, the conventional bush bearing 10 has a fixed outer diameter and the inner surface 11 defined by a bore thereof also has a fixed inner diameter. The outer diameter of the bearing 10 is slightly greater than the inner diameter of a central tube 13 of the stator 12. However, since the bearing 10 has a hardness lower than the central tube 13 (which is usually a metal tube or a plastic tube), it may be tightly fit into the central tube 13 in a mechanical manner.
The inner surface 11 defined by the bore of the bearing 10 is to receive the spindle 15 of the rotor 14 (such as a rotor fan). It should be noted that the bearing 10 is forcibly fit into the central tube 13 in a mechanical manner. Since the bearing 10 that has a lower hardness is subject to great fitting pressure, an irregular corrugation 16 is formed on the inner surface 11, as shown in FIG. 2. Thus, when the spindle 15 is inserted into the bore of the bearing 10, the spindle 15 forms only point contact engagement with the irregular surface 16 and no surface contact engagement may be obtained. This prevents the spindle 16 from forming a surface type friction with the inner surface 16 and due to the irregular corrugation of the surface 16, it can only have point contact with the spindle 15 and the resistance induced by the point contact is hard to control, resulting in an irregular rotation of the rotor so that the noise increases, the rotation becomes unstable and the operation life of the motor is reduced.